npm/marky-markdown

// markdown-it plugin to rewrite image and link URLs to be static github URLs
// when the calling code provides github repository information
//
var gh = require('github-url-to-object')
var URL = require('url')
var path = require('path')

var DEFAULT_REF = 'HEAD'

function buildImageUrl (repository, url) {
  var prefix = 'https://raw.githubusercontent.com/'
  return prefix + path.join(repository.user, repository.repo, DEFAULT_REF, url.href)
}

function buildLinkUrl (repository, url) {
  return repository.https_url + path.join('/blob/' + DEFAULT_REF + '/', url.href)
}

// search the provided HTML snippet and rewrite the attribute on the given tag
// using the repository object provided
function replaceTagAttribute (html, tag, attribute, buildUrl, repository) {
  // look for the attribute's value
  var regex = new RegExp('<\\s*' + tag + '[^>]*\\b' + attribute + '\\s*=\\s*', 'i')
  var attr = html.match(regex)
  if (attr) {
    // mark the location and figure out what kind of quotation mark is delimiting the value
    var position = attr.index + attr[0].length
    var quote = html.charAt(position)
    var substring = html.slice(position + 1)

    // now that we've found the first delimiting quotation mark, match
    // everything up to the next instance of the same quotation mark
    var src = substring.match(new RegExp('^[^' + quote + ']*'))
    if (src) {
      var url = URL.parse(src[0])

      // Skip fully-qualified URLs, #hash fragments, and protocol-relative URLs
      if (!url.host && url.path && !url.path.match(/^\/\//)) {
        var newUrl = buildUrl(repository, url)
        return html.slice(0, attr.index) + attr[0] + quote + newUrl + quote + substring.slice(src[0].length + 1)
      }
    }
  }
  return false // indicate that we did no replacement
}

module.exports = function (md, opts) {
  if (!opts) return
  if (!opts.package) return
  if (!opts.package.repository) return

  var repo = gh(opts.package.repository)

  if (!repo) return

  // rewrite image locations to be fully qualified github URLs
  var originalImageRule = md.renderer.rules.image
  md.renderer.rules.image = function (tokens, idx, options, env, self) {
    var src = tokens[idx].attrGet('src')

    if (src && src.length) {
      var url = URL.parse(src)

      // Skip fully-qualified URLs, #hash fragments, and protocol-relative URLs
      if (!url.host && url.path && !url.path.match(/^\/\//)) {
        tokens[idx].attrSet('src', buildImageUrl(repo, url))
      }
    }
    return originalImageRule.call(this, tokens, idx, options, env, self)
  }

  // rewrite link hrefs to be fully qualified github URLs
  var originalLinkRule = md.renderer.rules.link_open
  md.renderer.rules.link_open = function (tokens, idx, options, env, self) {
    var href = tokens[idx].attrGet('href')

    if (href && href.length) {
      var url = URL.parse(href)

      // Skip fully-qualified URLs, #hash fragments, and protocol-relative URLs
      if (!url.host && url.path && !url.path.match(/^\/\//)) {
        tokens[idx].attrSet('href', buildLinkUrl(repo, url))
      }
    }
    if (originalLinkRule) {
      return originalLinkRule.call(this, tokens, idx, options, env, self)
    } else {
      return md.renderer.renderToken(tokens, idx, options)
    }
  }

  function makeHtmlTransformer (originalRule) {
    return function (tokens, idx, options, env, self) {
      var content = tokens[idx].content
      var imgHtml = replaceTagAttribute(content, 'img', 'src', buildImageUrl, repo)
      var linkHtml = replaceTagAttribute(content, 'a', 'href', buildLinkUrl, repo)

      tokens[idx].content = imgHtml || linkHtml || content

      return originalRule.call(this, tokens, idx, options, env, self)
    }
  }

  // rewrite image locations in inline/block HTML as fully qualified github URLs
  md.renderer.rules.html_inline = makeHtmlTransformer(md.renderer.rules.html_inline)
  md.renderer.rules.html_block = makeHtmlTransformer(md.renderer.rules.html_block)
}